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ADC: Data Acquisition System

Sarang Suryawanshi
Prodigy 140 points
Other Parts Discussed in Thread: ADS8684, ADS8684A

Hello,

We are working on the design of data acquisition system.
Specifications are:
1. Number of analog input channel 4 ch. (single ended 4ch., differential 2ch.)
2. Input Range -10V to +10V, 0 to +5V.
3. Limit frequency (3dB) 10kHz/Through(200kHz) selectable (if possible)
Could you suggest any ADC that supports these specifications?

Alternatively, could you provide solution to this design.

Best Regards,

Sarang Suryawanshi

  • 0
    TI__Genius 14317 points
    Hello Sarang,

    Can you tell me what ADC resolution you require (how many bits) and if you need to simultaneously sample all 4 channels or if an ADC with an internal mux is acceptable.
  • 0 in reply to Jeffery Pfarr
    Prodigy 140 points
    Hello Jeff,
    Consider the following:
    4. ADC Resolution: 16-bit (minimum 14-bit)
    ADC with an internal MUX is acceptable (however other design is also welcome).

    Best Regards,
    Sarang Suryawanshi
  • 0 in reply to Sarang Suryawanshi
    TI__Genius 14317 points

    Hi Sarang,

    Please take a look at the ADS8684 and ADS8684A

    Note: If you are sampling in sequence on all 4 channels then the maximum throughput per channel is 125 KHz and the per channel input BW per nyquist is 62.5 kHz.

  • 0 in reply to Jeffery Pfarr
    Prodigy 140 points
    Hello Jeff,

    I am not sure if ADS8684, ADS8684A supports differential signal also.

    Best Regards,
    Sarang Suryawanshi
  • 0 in reply to Sarang Suryawanshi
    TI__Mastermind 46785 points

    Hello Sarang,

    Both ADS8684/8684A support single-ended true bipolar input ranges up to ±10.24 V, the difference between them: 

    1. Input ranges:

    ADS8684A support 9 input ranges which are Channel-Independent Programmable Inputs:

    • ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V
    • 10.24 V, 5.12 V, 2.56 V, 1.28 V

    but ADS8684 supports 5 ranges:

    • Bipolar: ±10.24 V, ±5.12 V, and ±2.56 V
    • Unipolar: 10.24 V, 5.12 V

    2.  Alarm feature:

    ADS8684A has one more feature:

    • ALARM → High and Low Thresholds per Channel

    Thanks.

    Regards

    Dale Li

  • 0 in reply to Dale Li
    Prodigy 140 points
    Hello Dale,

    Thank you for the reply.

    I am sure AD8684 supports single ended bipolar input range.
    However, wish to know if differential signal is also supported?

    Best Regards,
    Sarang Suryawanshi
  • 0 in reply to Sarang Suryawanshi
    TI__Genius 14317 points

    Hello Sarang,

    Unfortunately, the ADS8684 and ADS8684A only support single ended inputs, however there are single ended to differential stages in the device so that all channels drive the ADC differentially with the correct offset voltage being set.

    Again, pay attention to the input signal bandwidth as well (per my previous note). If all 4 channels are used and sequenced, the max channel BW for each channel is 62.5 kHz (sample rate 2x per Nyquist).

    If these devices will not work for this application, then the next best solution we have would be 4, single channel ADCs.

  • 0 in reply to Jeffery Pfarr
    Prodigy 140 points

    Hello Jeff,

    Thank you for the note. 

    What I understand after reading the note is as follows:

    My requirement for every channel from the specifications (in first post is):

    Sampling Rate(for every channel)= 2* Highest Frequency in the input signal= 2* 200K= 400Ksps

    So the required throughput for 4 channels= 400Ksps * 4= 1.6Msps.

    So, ADC with sampling rate>= 1.6Msps should do my work.

    Correct me if I am wrong.

    Best Regards,

    Sarang

  • 0 in reply to Sarang Suryawanshi
    TI__Genius 14317 points
    Hi Sarang,

    This would apply for a 4 channel multiplexed ADC (one ADC in the package) that samples the 4 channels in sequence. You could use 4 simultaneously sampling ADCs and then multiplex the data to get around this. Unfortunately, we do not have a quad channel multiplexed ADC that meets all of your requirements (# of bits, input levels/type etc.) and will sample at higher than 500 ksps.
  • 0 in reply to Sarang Suryawanshi
    TI__Mastermind 46785 points

    Hello Sarang,

    I'm Apps engineer from SAR ADC product line at TI, our team would like to take the discussion with you offline, I will send a email to you, thank you for your query on E2E forum.

    Best Regards

    Dale Li